1. Field of the Invention
The invention relates generally to the field of data transmission, especially to a flow control method of MAN (Metropolitan Area Network) transmission equipment.
2. Related Technology
In MAN devices based on a SDH (Synchronous Digital Hierarchy), data from users need to be mapped to the SDH for transmission. If data quantity transmitted from a sending end exceeds the processing capability of a receiving end, congestion will occur, thus flow control is required.
At present, for MAN transmission equipment, flow control is mostly implemented by adopting an Ethernet flow control mechanism based on a data transmission port, which is defined in IEEE standards. When data quantity in a buffer of data transmission port of a receiving end exceeds a specified maximum threshold, the data transmission port sends to the sending end a standard 802.3x flow control frame, and the sending end determines whether to end the flow control state according to a flow control time in the flow control frame. When the flow control time is up, data transmission is continued.
The flow control of 802.3x standard complies with a standard IEEE protocol, which is mature and easily implemented. However, in terms of flow control of this standard, it is determined whether to end flow control state according to the flow control time carried by the flow control frame, thus poor real-time quality occurs. On the other hand, the flow control of 802.3x standard is the one based on Ethernet data transmission port, so flow control for a transmission board and a mapping channel in an Ethernet Metropolitan Area transmission equipment cannot be implemented. With the number of boards and logical sub-channels in MAN transmission equipment increasing, the probability of congestion of board or logical sub-channels also increases. When congestion occurs in boards or logical sub-channels of receiving ends, the data transmission ports of sending ends will not pause data transmission to boards and logical sub-channels, thus leading to breakdown of boards or logical sub-channels, being unable to satisfy flow control service requirements of the complicated Ethernet Metropolitan Area transmission equipment.